1. Field of the Invention
The present invention relates to a technique of reducing electric power consumption in failure determination of a detection unit provided in an exhaust system of an engine of a hybrid vehicle.
2. Description of the Related Art
Among recently developed hybrid vehicles, a vehicle has been developed that allows a travel mode (series mode) in which an engine drives a motor generator to generate electric power and only an electric motor drives travel driving wheels.
Further, for the hybrid vehicle that allows the travel mode, a technique has been developed of performing failure determination of a detection unit (air-fuel ratio sensor, oxygen concentration sensor, catalyst monitor, or the like) in an exhaust system of an engine in the travel mode.
For example, Japanese Patent Laid-Open No. 2011-194976 discloses a technique of stopping fuel supply to an engine and performing so-called motoring in which a motor generator is driven using electric power supplied from a driving battery included in a vehicle to forcedly drive the engine, and while ensuring an exhaust flow rate of the engine, performing failure determination of a detection unit in each exhaust system from a change in a detection value of the detection unit due to the stop of the fuel supply.
However, in the failure determination as described above, to ensure determination accuracy, a high rotation speed has to be set in motoring so as to obtain a required exhaust flow rate.
Thus, electric power consumption due to the motoring performed in the failure determination may reduce a state of charge of the driving battery. Thus, to recover the state of charge of the driving battery after the failure determination, the engine has to be driven so as to increase an amount of electric power generation of the motor generator, which may reduce fuel efficiency.